As one travels through Texas and Oklahoma and other oil producing regions, it is common to see oil wells with rocking beam pumps in action. The beam is rocked like a seesaw by a motor while one end the beam lifts and lowers a sucker rod string to drive a pump positioned at or neat the bottom of the well. The sucker rod string is typically made up of a number of twenty-five foot to thirty foot steel rod sections connected end to end to form a long string of rods that extend down into the production tubing of a well. The production tubing itself was inserted into the wellbore after the wellbore was drilled and cased. The production tubing is fixed in the wellbore with a down hole rod pump positioned near the bottom. As the sucker rod moves up and down in the production tubing, the pump draws liquids from the wellbore into a chamber of the pump through a first check valve during a first stroke and then pushes the liquids in the chamber through a second check valve during the return stroke. The liquids pass through the second check valve and into the production tubing above the pump so that the liquids are eventually pumped to the surface and are either piped or trucked to market.
Natural gas wells and many low rate oil wells are sometimes provided with pumps to periodically withdraw liquids that enter the wellbore from the formation and tend to accumulate and slowly and eventually stop the production of hydrocarbons the natural gas. The liquid may be water, but may also include hydrocarbon liquids which are sufficiently valuable to collect and transport to market.
One of the problems associated with pump systems for small volumes of liquids in wells is that any solids, particularly fines and small particles, that are produced tend to collect and cause trouble for the pump. If the liquid volume were substantially higher, the particles would likely be carried to the surface and not collect at the bottom of the production tubing. With low liquid production rates and intermittent pumping, the particles tend to collect in the production tubing on top of the pump and have been known to damage the pumps and pumping systems well short of their expected service life. This can be especially challenging in coal seam gas production wells where the particles tend to be very fine and abrasive and are susceptible of stacking out rod strings by caking up and packing between plungers and barrels and blocking the travel of check valves and other vital pumping equipment. Coal seam gas wells typically produce water along with highly abrasive coal fines.
Many other wells produce sand which is a problem on a much larger scale in terms of total numbers of pumps exposed to particles. Some wells have sand delivered into the formation to hold open the fissures, fractures and perforations to enhance production of gas and liquids. This kind of sand is called proppant. Unfortunately such proppant sand causes many rod pump failures every year as some amounts exit the formation and creates hazard for moving equipment such as the pump in the wellbore. Another type of sand that is even more difficult for pumps to handle is formation sand, often referred to as flour sand. Formation sand is quite fine in nature and very difficult to control due to its fine size and mobility. It is highly abrasive and will wear out the polished surfaces of a pump or bury and stack out the pump.